1. Field of the Invention
The present invention relates to a solid electrolytic capacitor which includes a capacitor element hermetically sealed in a package made of synthetic resin. The present invention particularly relates to a surface-mount solid electrolytic capacitor to be mounted on a support member such as a printed circuit board by soldering, and to a method for manufacturing such a solid electrolytic capacitor.
2. Description of the Related Arts
Generally, a surface-mount solid electrolytic capacitor of the above-described type includes an anode lead terminal and a cathode lead terminal each projecting from a side surface of a package. With this structure, however, the size of the capacitor increases due to the projection of the two lead terminals from the side surfaces of the package, whereby the weight thereof also increases.
Recently, therefore, to reduce the size and weight of the capacitor, a surface-mount solid electrolytic capacitor is proposed which has such a structure as disclosed in JP-A-2003-67576. As shown in FIG. 11, the surface-mount solid electrolytic capacitor disclosed in the above-described publication includes a capacitor element 11, an anode lead terminal 12 and a cathode lead terminal 13 made of a metal plate, and a package 14 made of synthetic resin and hermetically sealing the entirety of the capacitor element 11. The lead terminals 12 and 13 are embedded in the bottom portion of the synthetic resin package 14 so that respective lower surfaces of the lead terminals 12 and 13 are exposed at the lower surface of the package 14. The capacitor element 11 is arranged on the upper side of the lead terminals 12 and 13. The capacitor element 11 includes a porous anode chip body 11a, and an anode bar 11b projecting laterally from the anode chip body. A stud 16 is integrally formed on the anode lead terminal 12, and the anode bar 11b is bonded to the upper surface of the stud 16 by welding. A cathode film 11c is formed on the periphery of the anode chip body 11a of the capacitor element 11, and the cathode film is bonded to the upper surface of the cathode lead terminal 13 by conductive paste 15.
In the capacitor element 11, the bonding of the anode bar 11b, which projects from the anode chip body 11a, to the upper surface of the stud 16 on the anode lead terminal 12 is performed by resistance welding described below.
First, as shown in FIG. 12, the cathode film 11c of the capacitor element 11 is bonded to the cathode lead terminal 13 by conductive paste 15. The anode lead terminal 12 is placed on a welding receive electrode 17. In this state, the anode bar 11b is pressed against the stud 16 by a welding press electrode 18. By flowing current between the welding receive electrode 17 and the welding press electrode 18, the anode bar 111b and the stud 16 are resistance-welded.
However, in the above-described resistance welding, the press electrode 18 (and/or the receive electrode 17) may deviate from the stud 16 in the axial direction of the capacitor element 11 (horizontal direction in FIG. 12). Specifically, the press electrode 18 may deviate in the direction away from the capacitor element 11 (See FIG. 12) or in the direction toward the capacitor element 11 (See FIG. 13).
In the instance shown in FIG. 12, the corner portion of the stud 16, which is farther from the capacitor element 11, melts first. In this state, the anode bar 11b is pressed downward by the press electrode 18. Therefore, a force in the counterclockwise direction is exerted on the anode bar 11b. As a result, as indicated by the double-dashed line in the figure, the capacitor element 11 rises from the cathode lead terminal 13, and the cathode film 11c bonded previously is separated from the cathode lead terminal 13.
In the instance shown in FIG. 13, the corner portion of the stud 16, which is closer to the capacitor element 11, melts first. In this state, the anode bar 11b is pressed downward by the press electrode 18. Therefore, a force in the clockwise direction is exerted on the anode bar 11b, so that the capacitor element 11 is excessively pressed against the cathode lead terminal 13. As a result, as indicated by the broken line in the figure, the left end of the anode bar 11b may be warped upward. In this case, dielectric breakdown occurs at the anode chip body 11a and/or the anode bar 11b. 